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Residential Truss Repair Advice

Residential Truss Repair Advice

Residential Truss Repair Advice

(OP)
I need some advice on a truss repair at my resident.

Some background.  The area of repair had a roof leak, and previous owner let it sit and rot.  I discovered the problem when I had to rework some electrical conduits in the attic, so I removed some ceiling sheetrock and found that the heel of one truss has completely disintegrated - meaning I can break pieces of the wood off with my bare hand.  Here is a simple illustration.  The dashed line section were rotted away.



The good news is, it appears to have been in this condition since 2004, and the roof has not sagged.

I took a recipricating saw and cut back to where I have solid wood, then I supported the joist with a double 2x4.

My first thought was to put in new 2x4s to replace the missing sections, then use plywood gussets on both sides.  However, with both the rafter and joist missing a short piece, this may not be good enough.  I decided to sandwich the original rafter and joist on both sides with new 2x4s.

First, I nailed a sheet metal plate from the back side to the original joist.  Then I put a 10 feet piece of 2x4 behind it.  Nailing the other half of the metal plate to the new 2x4.  Then I did the same to the rafter and attached a new 2x4 behind it.  I nailed the old and new wood together with 3" 10d nails spaced every 10" or so.  This is depicted below.  The original 2x4 is of darker color, the piece behind it is the new sister 2x4.



A closer view.





Next, instead of putting in new 2x4s to connect to the original wood members, I cut two sheets of 3/4" marine grade plywood to the shape as shown below.



The two sheets of 3/4" plywood results in the same thickness as a 2x, and is more rigid because it's made out of one piece.  I plan to glue the plywood to the new 2x4 behind it, then nail it together with 3" 10d nails, as shown below.



Then I plan to put in another 2x4 joist and rafter to the front of it, nail them in place, then drill 3/8" holes through all three wood members every 24", and use 3/8" bolts with large washers and nuts tightened from both ends.  The plywood sections would be in the middle when I am all done.

Would appreciate any comments on the approach and what I could do better.  I think this gives it the best support.  Thanks in advance.

RE: Residential Truss Repair Advice

Unless the truss has an interior bearing mid-span or closer to this end of the truss your repair does not come close to meeting the code requirements. Your temporary support also should be at a truss panel point at least and hopefully this is a single story house. If your state allows non-engineers to design homes, than you need to analysis the forces in the truss than nail, screw, bolt for the forces per the NDS. If your state does not allow non-engineers to design homes or you are unable to do the required calculations than you need to hire an engineer.
On your side, the truss has remained standing for some time with this condition.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Residential Truss Repair Advice

(OP)
It has been this way for a long time (6 plus years) so there is some redundancy.

I am a licensed engineer but my area of specialty is on drainage and roadway design, structures is not my thing and I vaguely remember my moments and shear calculations during my college days.

I guess my point is, with this particular truss, and I think the pictures showed the amount of conduits and pipes that pass between the joists and rafters I am limited with what is possible.

There is nothing supporting this truss in mid span or anywhere in between.  However, the next truss over (as can be seen in the first picture) is a double truss, two 2x4 together, then another 2x4 truss 24" over,followed by another one, then another double 2x4 in that pattern.  I think this is why the rotted truss has not cause a sag, the double truss next to it has absorbed the load.

RE: Residential Truss Repair Advice

(OP)
By the way, this is a single story.  Forgot to mention that.  Location is Miami, Florida, and the existing truss is of southern yellow pine.

RE: Residential Truss Repair Advice

The plates would be connected essentially to transfer shear at the interface of the top and bottom chord.

A measure of this force could be determined from the connection plate just inboard from the point of support.

CCMC has tabluated values for plates based on shear, tension, and grip.  In addition for there being values for parallel and perpendicular to the grain for the lumber, there are also values based on the orientation of the 'teeth'.

Your plywood gusset idea is pretty sound, going back to 'real wood', not rotted... check with a nail, screwdriver, awl, or pocketknife to determine the extent of damaged wood, and carry your gusset well beyond that.  

I'd secure the gusset with Bulldog PL adhesive... not nails or screws..

Dik

RE: Residential Truss Repair Advice

Please understand that you are doing the repair completely wrong. You need at least an equal area of the gusset onto the top and bottom members and you don't have this as they are placed in your pictures. The bottom member should of been cut snug to the bottom edge of the top member not the top member being cut to the top edge of the bottom member. Whether you can get enough area for the force (shear and tension of the gusset is also very important to check for) transfer is questionable even if you correct this problem with the limited area you have to work around. You will also need to jack up the damaged truss before repairing it to get the forces back into it and out of the adjacent trusses which this force is now being transfer to by the roof sheathing.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Residential Truss Repair Advice

Woodman....   Reread his entire posts, and see if you don't agree, I think he's heading in the right direction.  The plywd. is just a filler to fill in the 2x (1.5" thick mat'l.) which he cut out.  Otherwise he is sistering new 2x4 top chord members about 10' long on to both sides of the existing truss top chords; and sistering new 2x4 bot. chord members about 10' long on to both sides of the existing truss bot. chords.  A triple wide truss on this end.  The exact lengths and lumber grade of the sister mat'l. may be an issue to study a bit.  The trick now is to make the proper connections btwn. new and old and btwn. the new top chords and new bot. chords at the heal or bearing point.

Miamicuse....  I would like to know more about why every other existing truss is doubled, so your're not missing something.  I would prop that truss up to take most of the load off the bearing end while you are making this fix, and as Woodman suggested the primary props should be at bot. chord panel points, similar to the double 2x4 post you show.  But, your prop just tends to bend the bot. chord.  Note that what you call a rafter, I call a top chord; and what you call a clg. jst. I call a bot. chord of the truss.  You must design a steel nailer pl. connection btwn. your new top chords, and your new bot. chords, across the horiz. cut on the top chord to the bot. chord.  The truss forces, from a truss analysis, will dictate the forces at that connection.  And, what Dik was explaining applies to the design of these nailer plates.  And you must tie your new chord members into the old to transfer the truss forces in those members.  I would use glue, clamps, and lots of nails, and forget the nuts and bolts.  You must pay attention to edge distances, end distances and nail spacing, both lengthwise and across the grain.  In this case, many smaller connectors from both sides, 16d or better yet 20d nails will work better than bolts would.

RE: Residential Truss Repair Advice

Unless I'm missing something, I would use an anti-fungal coating to 'kill' the rot, and leave the existing material in place, replacing the metal truss plates with plywood gussets, extending surriciently to sound material and glue the gussets in place.  Adhesive strength is significantly stronger than the metal plates and/or nails...

Dik

RE: Residential Truss Repair Advice

Judging from the location of the top chord at the heel, I would move the post to line up with the top chord panel point and neatly fit some solid blocking between it and the bottom chord to alleviate load from the top chord going to the heel.

Dik

RE: Residential Truss Repair Advice

dhenger, I did read the post. The problem is not the connection of the new 2x's to the old 2x's. The problem is connecting the new top and bottom 2x's for force transfer at the bearing. The best way to achieve this is having an equal amount of area of the top and bottom members to connect a gusset to.
This is the "trick" as you said and which I tried to address in my posts above.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Residential Truss Repair Advice

(OP)
Let me answer a few questions.

On jacking up the truss to transfer the load.  This has already been done.  After I cut the rotted wood sections out, even though there is no sag in the roof deck and nearly framing - and I checked with a level and strings.  I know with the heel completely gone I need to put it back in it's original configuration and angle.  I used a bottle jack and a 4x4 beam to move up the bottom chord by about 1/4" from level.  I then hammer in place the double 2x4 temp support that you see now and removed the bottle jack.  This support is going to be removed once I am done.  I also jacked up the top chord a little from where I had that temp support.  I then attached the two 8' 2x4s to the truncated top and bottom chords.

Regarding the metal plate, it was there initially to attach the bottom chord to the new sister 2x4.  I realize it is not going to work, it's just a temp mending piece.

About the rot treatment.  I cut back the bottom chord to where I had solid wood 100%.  The top chord I didn't cut all the way back, I undershot it by about 1.5" because there is a member crossing above it and at the time I felt I needed that there.  I did brush on Abatron Liquid Wood into the rotted portion and filled in some Wood Epoxy.  It is only the last 2" that is still partially rotted up top.

Woodman88 mentioned that the way I had the 2x4 sistering the top/bottom chord is wrong, let me make sure I understand fully.  I think you are saying that I should be doing illustration "A" and not "B", right?



I think it is extremely difficult to take this out now because I have nailed the members together at close intervals, I believe if I try to remove it now, all the prying and pulling will result in more weakening of the original chords.  However, may be I can find a way to connect them that will help?  Can I drill a vertical hole from the new sister top chord, through the bottom chord, through the top plate of the bearing wall, and use bolts to secure them tightly, or insert another piece between this top chord and the bottom of the roof deck to wedge it in?  Also, since I have not yet put in the front 2x4 to sister it, I could certainly cut the front members the right way.

As far as using the right terminology, my apologies.  I tried to go back and see if I can edit it, but not any more, I will use the proper terms from now forward.

My first instinct upon seeing this situation, is to use large triangular gusset pieces to mend the chords at the heels and extend that as far up the truss as possible.  However, as you can see with all the electrical conduits, this is just not possible.  That lead to the "contraption" approach I have now.

To dhengr, about your question on the double truss, let me elaborate.  It is not every other one, what I wrote initially may have been confusing.  What it is as you go further to the right, I have a fire place.  All the trusses heading to the fire place (three of them), instead of attaching to the mason wall of the fire place, they attach directly to a double set of 2x10s.  This double 2x10s "hangs" on to double trusses on both ends, as shown below.





and yes, the gusset plywood pieces I have is a filler piece between the new 2x4 members sandwiching the original top and bottom chords.
 

RE: Residential Truss Repair Advice

Illustration "A" will double the area to the top member for the connection of the top to bottom member. Also the more nails or connecting material you can get into the top chord over the bearing will reduce the amount of moment in the gusset and its connetions.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Residential Truss Repair Advice

(OP)
woodman88, you said the more nail and connection materials the better.  Is it true that more nails but smaller nail size is better then bigger stronger nails (like 10d) but fewer?

If so how do you attach the nails?  I was using an air palm nailer.  I plan to use both nails and adhesive as dik suggested above.  However, I can only attach where the 2x4 footprint overlaps with the plywood, which is limited.

I wonder, once the triple ply 2x4 are all said and done, would it help strengthen the rigidity of the heel joint if I add two more layers of ply outside of the sistered wood further up from where the pipes are.  I am not sure it would.



Another idea I have been thinking, is some sort of custom fabricated sheet metal that wraps the whole three ply heel in one piece on the outside of what I have.

RE: Residential Truss Repair Advice

I didn't say 10d nails, I said 16d or 20d nails and glue to get a nail length that would tie all three chord members together.  My comment 'more smaller connecters is better than fewer big connecters' was referring to nails vs. your bolts, in this repair.  Bolts just don't work real well in these types of applications, as the joints must move a bit to bring the bolts into bearing in the holes.  At the bearing (or heel), the top chord is in compression and the bot. chord is in tension, and the connection you design and build must reconcile (resolve) these forces across the joint btwn. the two chords at that point, the heel.  Which ever detail you use A or B, and I think I do see Woodman's point about using A, and getting more gusset length on the top chord, given the plywd. gusset you could cut and fit; You must get enough nails into the top chord to take its compression, you must get enough nails into the bot. chord to take its tension; and these forces must be resolved and transferred through the plywd. gussets or through metal nailer plates, and there must be enough length to do that.  8d or 10d nails might be fine for attaching a gusset or nailer plate across that heel joint and into the chord members.  All of this to meet code and design strengths for the materials you use, of course.
 

RE: Residential Truss Repair Advice

(OP)
dhengr, thanks for the clarification.  I was thinking a bolt with large washers and nuts would bind the three layers of 2x together tighter than nails would.  I had planned to use adhesive, nails and bolts - all three.  I think you are saying skip the bolts, but use more nails to penetrate all three layers.  I can do that.

RE: Residential Truss Repair Advice

(OP)
All the feedback I have gotten so far have me thinking.

I saw this article about marine grade epoxy by West System.  In this article they talked about embedding a rebar inside a wood beam secured with epoxy.

http://www.westsystem.com/ss/beam-me-up-2/

I am wondering, instead of the two ply gusset that I had intended to put in the middle, would it create a better and more rigid joint if I do the following instead:

(1) cut the same shape out of a solid piece of 2x10.
(2) Drill a 1/2" hole 6" into the existing truncated top chord along it's length.
(3) Drill another 1/2" hole 6" into the existing truncated bottom chord along it's length.
(4) Drill two holes 6"deep into the edge of the 2x10 shape, in alignment with the holes in the existing chords.
(5) Epoxy into the holes two pieces of 1/2" rebar, then slide and hammer the rebars into the opposing holes in the existing chords (already filled with epoxy).

Will this mending with the metal rebar provided a more rigid and superior joint for my situation?  Or this is a bad line of thinking?

RE: Residential Truss Repair Advice

(OP)
Here is an illustration of what I am thinking to achieve a more rigid joint at the heel.

RE: Residential Truss Repair Advice

Miamicuse...your house was obviously built before the current wind load requirements in your area (plywood decking, darkened wood, old staining).  Your wind load requirements have increased quite a bit over the years (although the older houses performed better in Hurricane Andrew than the newer ones).

Nevertheless, you need to make sure your repairs are consistent with the uplift and lateral load needs in your area.

I have designed repairs for exactly this condition for condominiums in Jacksonville and Orlando.  I'll post a sketch...just don't have it on this computer.  

RE: Residential Truss Repair Advice

Solid 2x lumber is a very poor choice for use as a gusset. Plywood alternates the plys by 90 degrees and OSB glues small pieces together in all directions within the plane giving better strength in all directions. Solid lumber fibers are all basicly in the same direction and is more likely to split.
For all the work you are looking at, along with trying to do the repair correctly, I would contact a truss manufacterer about having them field press (as it will need to be pressed inplace as you will not be able to insert it without removing the roof sheathing or pipes) a repair jack frame to nail to your truss. They can also give you a uplift and member forces for the connections.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Residential Truss Repair Advice

Agree that adhesive joints are going to do more for you than nailed-only plates and gussets.
Resorcinol glue is WAY better than any stuff (garbage) that comes out of a caulking tube.  It's not real expensive and is worth your consideration.
Just my 2 cents on one minor aspect of the project, I'm no structural engineer by any stretch of the imagination.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Residential Truss Repair Advice

orneryone... give Bulldog premium a shot... really good adhesive and comes out of a tube... can glue steel to wood for reinforcing...

Dik

RE: Residential Truss Repair Advice

Thanks for that Dik, that's one I didn't know about.  I'll give it a try.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Residential Truss Repair Advice

My problem with using adhesives with gussets repairs is the that the adhesive is only connecting with the wood fibers in the plane between the 2x member and the gusset. The adhesive acts IMHO as a vise to the fiber. Which is like putting a wire in a vise and bending it back and forth. As long as the force is only in the elastic range you are okay. If it goes into the plastic range it breaks. Now adhesives work great when you have multiply surfaces like in plywood, OSB, finger joints, but for gusset repairs of wood trusses I only use it in addition to nails or staples.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Residential Truss Repair Advice

Woodsman... Just overglue it... a square inch of most good adhesives are equivalent to a mouthful of nails... Can easily take the adhesive value down to the 'rolling shear' capacity of plywood.

You can use nails to secure the adhesive <G>... on many repairs, I have relied on the adhesive strength with a few nails to hold it in place...

Dik
 

RE: Residential Truss Repair Advice

(OP)
Woodman88, my thought about using solid 2x10 it will not be acting as a gusset anymore, it will be using the rebars to strengthen where the members were cut off, and the connection at the heel is one single piece, so there is no concern about pattern A or B anymore.

This is a tricky project, so I am going very slow, I have other projects on going and this one I am taking baby steps and thinking it through as I don't want to rush it then regret later if there is a better approach.

I don't want to open the roof or relocate those pipes though...

Sometimes too much google can make things more confusing...LOL...

RE: Residential Truss Repair Advice

Miamicuse, So basically you are going to take the shaped 2x10 and hang it vertically from a vise at the lower rebar. Then hit it at the upper rebar with a big hammer every time you have a wind storm while hanging a large load from the upper rebar between storms. And you expect this to last how many years? Maybe it will maybe it won't. I will stick with the conventional wood truss repairs and tell you to move the pipes or get a field made truss frame for the repair.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Residential Truss Repair Advice

Dont forget the truss attachment (hurricane clips) and the top cord sag (before you nail it).  

Garth, FL law does allow homeowner engineering for your personal home (Dade county will not).  But no reason to get Dade county involve..  lol

RE: Residential Truss Repair Advice

boo1, Hopefully the law in FL also requires the homeowner to meet the minimum requirements of the building code.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Residential Truss Repair Advice

(OP)
Ron, thanks for the offer to post your repair design.  I look forward to it.

RE: Residential Truss Repair Advice

(OP)
I had a friend who is a bridge engineer look at this and here is his suggestion.

Take good measure and have a truss company fabricate a new heel with same measurements and go up about 4 feet or so on the top and bottom chord.

Then cut the existing top and bottom chords back.  Install new 2x4 headers going from the previous truss to the next truss at the top and bottom chords.  Then connect the broken top and bottom chords to the new headers, on both sides, using joist hangers.

Then ask the truss company for advice on how to reinforce the header connections to the adjacent trusses.

In my case, this is the last truss, so the "previous" would be a concrete wall, and the next is a double truss.

Any merit to this approach?

RE: Residential Truss Repair Advice

Your original repair would have functioned perfectly in this (minimally loaded) use.  The number and spacing of fasteners may have been weaker or stronger than needed, which is where the NDS comes in handy.

Feel free to complicate the repair as much as you like, but it is not really necessary for your own household use, for a roof which is not designed to take hurricane winds (which it appears yours is is not.)

It seems that the nearby gable end wall probably has taken the load since the damage occurred, if not before.  The tributary width to this truss appears to be very narrow, resulting is low loading and low demand.

As pointed out, glue works well, but 1) you cannot assure development of the entire section through surface bonding only, and 2) adhesives are not recognized by the building codes for this application.  So glue as you like (wood glue or a non-creep acrylic - 3M only makes one that is structurally rated and it is $$ per tube), but nail or bolt as well.  Truth be told, it is nearly impossible to get full strength connections in reasonably-sized wood truss gussets without bolts, but that might not be necessary here.

Go back to your original design, which provided two 2x4 sisters for each rotted 2x6 member, and a tight-fitting filler (the plywood.)  Bolt it all together, and call it a day.   

RE: Residential Truss Repair Advice

TXStructural, Per the 2009 IBC Section 2304.9.4 Other fasterners The use of glue are permitted where approved.
What section of the IBC (or other building code) are you looking at that states it is not recognized for truss repairs?
Also, I have design repairs for a great many wood trusses and have always used nails/staples (sometime with the addition of glue) but never bolts or glue alone to connect plywood/OSB gussets to the wood members.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Residential Truss Repair Advice

(OP)
Ron, thank you for your design.  I understand it however after considering for a while I can't implement it because it means I have to move all the metal conduits and this would be huge project.

RE: Residential Truss Repair Advice

miamicuse...slot the plywood around the conduit.  It will still work.  The plywood holds the plane and prevents lateral displacement.

RE: Residential Truss Repair Advice

(OP)
TXStructural, how did you determine that the roof was not designed to take hurricane wind?  Was it the lack of hurricane strap ties?

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